1. Field of the Invention
The present invention relates to a lithium secondary battery comprising a positive electrode, a negative electrode, a non-aqueous electrolyte comprising a non-aqueous organic solvent and a lithium salt, and more particularly to a lithium secondary battery comprising a positive electrode comprising a positive electrode active material of a three-component system and a non-aqueous electrolyte comprising an additive for deactivating a transition metal comprised in the positive electrode active material, thereby improving a cycle lifetime and preventing the lithium secondary battery from swelling phenomenon.
2. Description of the Related Art
Recently, as the application field of an energy storage technique is enlarged to a cellular phone, a camcorder, a notebook PC along with an electric vehicle, researches on the high energy densification of a battery employed as an electric power source of electronic devices have been actively conducted.
A lithium secondary battery developed during the early 1990s comprises a negative electrode made by using a carbon material capable of absorbing and desorbing lithium ions, a positive electrode made by using a positive electrode active material and a non-aqueous electrolyte comprising a lithium salt dissolved in a mixed organic solvent.
Recently, as the utilizing range of the lithium secondary battery is enlarged, requirement on lithium secondary batteries maintaining good properties at a severe environment comprising a high temperature and a low temperature, and capable of stable charging at a high voltage is gradually increasing.
Meanwhile, the capacity of the positive electrode active materials may be increased as a charging potential increases, however, the desorbing of the transition metal oxides constituting the positive electrode active material also may be accelerated to induce a structural instability.
In addition, organic solvents used as the non-aqueous electrolyte of the lithium secondary battery such as ethylene carbonate, propylene carbonate, dimethoxy ethane, γ-butyrolactone, N,N-dimethyl formamide, tetrahydrofuran or acetonitrile may be oxidized by emitted transition metal oxides and generate a gas when stored at a high temperature for a long time. Due to the generated gas, a battery assembly (battery parts) may be deformed to induce an internal short, and the battery may be deteriorated. In severe cases, the battery may be ignited or exploded. The oxidation reaction of the electrolyte may be accelerated as the amount of the transition metal eluted under high voltage conditions increases.
In order to solve the above-described defects, a method of adding an additive such as succinonitrile in the non-aqueous electrolyte has been suggested. In this case, the swelling phenomenon of the battery may be improved to some, however, the charge/discharge cycle lifetime of the battery may be decreased (Patent Literature 1).
Thus, there is a need to develop a technique for improving the safety of lithium secondary battery.